Conventionally, a flywheel is attached to a crankshaft of an engine for absorbing vibrations caused by variations in engine combustion. Further, a clutch device is arranged on a transmission side (i.e., in a position axially shifted toward the transmission) with respect to the flywheel. The clutch device usually includes a clutch disk assembly coupled to an input shaft of the transmission, and a clutch cover assembly for biasing the frictional coupling portion of the clutch disk assembly toward the flywheel. The clutch disk assembly typically has a damper mechanism for absorbing and damping torsional vibrations. The damper mechanism has elastic members such as coil springs arranged to compress in a rotating direction.
A structure is also known in which the damper mechanism is not arranged in the clutch disk assembly, and rather is arranged between the flywheel and the crankshaft. In this structure, the flywheel is located on the output side of a vibrating system, in which the coil springs form a border between the output and input sides, so that inertia on the output side is larger than that in other prior art. Consequently, the resonance rotation speed can be lower than an idling rotation speed so that damping performance is improved. The structure, in which the flywheel and the damper mechanism are combined as described above, provides a flywheel assembly or a flywheel damper. Such a structure is disclosed in Japanese Unexamined Publication H04-231757, which is hereby incorporated by reference. The flywheel fixed to the crankshaft of the engine is called a first flywheel, and the flywheel connected to the crankshaft via the elastic members is called a second flywheel.
The damper mechanism used in a dual-mass flywheel has an input member, an output member, and a plurality of elastic members for elastically connecting both members. The input member is a disk-like member formed with a plurality of window holes for accommodating the elastic members. The output member is composed of a pair of disk-like members disposed axially on the opposite side of the input member. The friction resistance generation mechanism generates friction resistance when the input member and the output member rotate relative to each other to compress the elastic members in the rotational direction.
The second flywheel is supported by the crankshaft via the elastic member in the radial direction and axial direction to be movable in each direction. Therefore, when a clutch release load is applied by the clutch device to the second flywheel, the second flywheel moves toward the engine in the axial direction. It is necessary to support the second flywheel by a member on the crankshaft side. In the prior art, however, the support portion has a complicated structure so that it is difficult to provide flat surface to support the second flywheel stably.
The friction resistance generation mechanism includes a plurality of washers disposed axially between the radially inner portions of the input member and the output member. For example, the friction resistance generation mechanism has a friction washer contacting input member, a friction plate engaging with the output member, and an urging member elastically compressed between the output member and the friction plate to urge both members.
As mentioned, the friction generation mechanism includes a friction generation surface on an axial surface of the input member. It is difficult to provide a long radius for the friction generation surface because the elastic member occupies a space in the input member. As a result, there is pressure against each of the members on the friction surface, and thus, the friction washer is quickly worn.
The elastic members are typically coil springs, which have a certain axial length. Therefore, if the elastic members are located in a position where they overlap a friction surface of the second flywheel, the portion of the whole structure becomes too large. In order to solve that problem, a structure is known in which the elastic members are located radially inward of the friction surface of the second flywheel. In that structure, the portion where the axial length is large is not formed. It should be indicated however, that it is impossible to provide a large enough stopper torque by just having one kind of the elastic members.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved flywheel assembly. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.